川渝湘鄂薄皮构造带多层拆离滑脱系的岩石力学性质及其对构造变形样式的控制

    Rock mechanical characteristics of the multi-layer detachment fault system and their controls on the structural deformation style of the Sichuan-Chongqing-Hunan-Hubei thin-skinned belt, South China

    • 摘要: 川渝湘鄂多层拆离推覆构造发育于秦岭-大别造山带、雪峰山厚皮构造带与四川盆地之间。这个薄皮构造带是在晚中生代沿一系列岩石薄弱层从南东向北西多层拆离滑脱构造作用下形成的,然而单纯的地表构造地质调查无法揭示各滑脱层是如何控制区内褶皱-断层关系的。因此,对拆离滑脱层进行识别是认识区内构造样式及其成因机制的关键。利用单轴岩石力学实验方法,对取自区内沿达县-大庸地质剖面不同岩性地层组合的样品进行岩石力学分析,并结合前人在区内已经获得的数据,结果表明区内至少发育5个可能的区域性拆离滑脱层。这些滑脱层主要由泥质岩、粉砂岩和泥质灰岩组成的,分别沿下寒武统牛碲塘组(Det I)、下志留统罗惹坪组和龙马溪组 (Det II)、下二叠统栖霞组(Det III)、下三叠统大冶组(Det IV)和中三叠统巴东组 (Det V)发育。野外调查表明,Det I控制了深部构造层次的断弯褶皱和叠瓦扇, Det II 可能控制了中部构造层次的断展褶皱和拆离褶皱,Det III则可能与Det IV和Det V一起,共同控制了上部构造层次的侏罗山式褶皱。

       

      Abstract: The Sichuan-Chongqing-Hunan-Hubei multi-layer detachment thin-skinned belt is developed between the Qinling-Dabie orogenic belt and Xuefeng thick-skinned belt and the Sichuan basin. This thin-skinned belt formed by NW-directed detachment of a number of Late Mesozoic rock layers of weakness. However, traditional surface geological survey along cannot reveal how various detachment layers control the relation between folds and faults in the study. Therefore, identification of the detachment faults at depths is the key to understanding the structural styles and their formation mechanism in the area. The authors used the uniaxial rock mechanical methods to test the rock samples from variable layer of the thin-skinned belt along a geological section from Daxian to Dayin. The test results together with previous published data reveled at least five possible regional detachment layers. These layers are mainly composed of pelite, siltstone and argillaceous limestone, distributed along the Lower Cambrian Niutitang Formation (Det I), Lower Silurian Luoreping and Longmaxi formations (Det II), Lower Permian Qixia Formation (Det III), Lower Triassic Daye Formation (Det IV) and Middle Triassic Badong Formation (Det V) respectively. Field survey further proved that: Det I controls fault-bend folds and imbricate fans in the deep tectonic level, and Det II probably controls fault propagation folds and detachment folds in the middle tectonic level, and Det III probably together with Det IV and Det V controls the Jura-type folds in the shallow tectonic level.

       

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